This exists because reduceByKey needs K and V to be members of
the ClassTag type class, but adding that restriction to the type
parameters of the class above would break the API.

This exists because reduceByKey needs K and V to be members of
the ClassTag type class, but adding that restriction to the type
parameters of the class above would break the API. Neither method
can be named toSpatial as that would hide the methods provided
by the class above.